Chiral MnIII–salalen and –salan Complexes Derived from (S)‐Pyrrolidin‐2‐ylmethanamine and Their Catalytic Activity in the Asymmetric Strecker Reaction

Abstract

AbstractThe salalen and salan ligands have been synthesized by the reactions of (S)‐pyrrolidin‐2‐ylmethanamine and salicylaldehyde derivatives. These ligands were treated with Mn(CH3COO)2·4H2O followed by air oxidation to give (S,R)‐MnIII–salalen and –salan complexes in yields of 84–88 %. The absolute configuration of (S,R)‐MnIII–salalen was determined by single‐crystal X‐ray diffraction and CD analysis of the ligands and complexes showed similiar Cotton effects. The MnIII–salalen and –salan complexes were screened for their catalytic activity in the asymmetric Strecker reaction. (S,R)‐2,4‐Di‐tert‐butyl‐6‐({[1‐(3,5‐di‐tert‐butyl‐2‐hydroxybenzyl)pyrrolidin‐2‐yl]methylimino}methyl)phenolatomanganese(III) chloride (5 mol‐%) was found to be a suitable catalyst for the asymmetric Strecker reaction of N‐(4‐methoxybenzylidene)diphenylmethanamine with ethyl cyanoformate, which gave 89 % yield and 55 % ee of 2‐(benzhydrylamino)‐2‐(4‐methoxyphenyl)acetonitrile at –15 °C after 24 h.